Instrument panel radio antenna

ABSTRACT

In an automotive vehicle including an instrument panel assembly located beneath a windshield opening enclosed by a conductive body structure which forms a radio wave shield, a conductor is supported by a nonconductive top portion of the instrument panel assembly for inductively collecting radio waves passing through the windshield opening from outside of the vehicle thereby to provide a broadband antenna for an AM/FM radio receiver mounted within the instrument panel assembly.

United States Patent [191 Killen et al.

[ INSTRUMENT PANEL RADIO ANTENNA [75] Inventors: Charles W. Killen, Piqua; Robert W.

Forward, Centerville, both of Ohio [73] Assignee: General Motors Corporation,

Detroit, Mich.

[22] Filed: June 11, 1973 [21] Appl. No.: 368,540

[52] US. Cl 343/713; 180/90 [51] Int. Cl. H0lq 1/32 [58] Field of Search 343/711, 712, 713; 180/90 [56] References Cited UNITED STATES PATENTS 1,855,155 4/1932 Sampson 343/908 2,094,168 9/1937 Forbes 343/713 2,520,985 9/1950 Williams et a1... 343/712 2,774,811 12/1956 Shanok et al. 343/711 3,088,539 5/1963 Mathues et a1... 180/90 3,635,305 1/1972 Kunishi et al. 180/90 July 22, 1975 FOREIGN PATENTS OR APPLICATIONS 1,237,187 6/1960 France 343/713 734,171 4/1943 Germany 343/713 1,197,127 6/1959 France 343/713 Primary Examiner-Eli Lieberman Attorney, Agent, or Firm-T. G. Jagodzinski [57] ABSTRACT In an automotive vehicle including an instrument panel assembly located beneath a windshield opening enclosed by a conductive body structure which forms a radio wave shield, a conductor is supported by a nonconductive top portion of the instrument panel assembly for inductively collecting radio waves passing through the windshield opening from outside of the vehicle thereby to provide a broadband antenna for an AM/FM radio receiver mounted within the instrument panel assembly.

1 Claim, 3 Drawing Figures PATENTED JUL 2 2 I975 INSTRUMENT PANEL RADIO ANTENNA This invention relates to a radio antenna for an automotive vehicle.

In general, two forms of automotive radio antennas find prevalent usage today: namely, the mast antenna and the windshield antenna. The mast antenna comprises a rod conductor projecting vertically from the vehicle body. In such an exposed location, the mast antenna is subject to deterioration by the weather elements, it is prone to damage from striking against external objects, and it is easy prey for the perverse handiwork of vandals. Further, the mast antenna is thought by some to detract from the aesthetic appearance of the vehicle. Of course, the mast antenna can be made to automatically retract within the vehicle body, but such an auxiliary powered arrangement contributes some extra cost to the antenna.

In the windshield antenna, one or more very thin conductors are embedded within the windshield of the vehicle. Consequently, the conductors of the windshield antenna are, to a degree, shielded from the previously identified destructive forces lurking outside of the vehicle. However, the windshield antenna is somewhat susceptible to various forms of FM distortion, particularly station swapping, and it is somewhat sensitive to changes in the direction of vehicle travel. Moreover, operation of the windshield wipers can have several undesirable effects upon the performance of the windshield antenna including the generation of noise. Lastly, the conductors of the windshield antenna inevitably add to the cost of replacing a damaged vehicle windshield.

The present invention remedies many of the aforementioned problems associated with the mast and windshield antennas, and it provides some unique advantages not attainable by either the mast antenna or the windshield antenna.

In a preferred embodiment of the invention, an automotive vehicle includes a conductive body structure having a windshield aperture through which radio waves otherwise shielded by the body structure may enter the vehicle. An instrument panel assembly includes a nonconductive instrument panel pad having a top portion located beneath the windshield opening of the vehicle such that radio waves entering the vehicle through the windshield aperture irradiate the top portion of the instrument panel pad. An antenna conductor is supported by the top portion of the instrument panel pad for inductively collecting passing radio signals thereby to provide a broadband antenna for an AM/FM radio receiver mounted within the instrument panel assembly.

The instrument panel radio antenna of the invention yields a number of important advantages.

First, the instrument panel antenna is relatively insensitive to the direction of vehicle travel and it is rela tively unencumbered by many of the common forms of FM distortion, especially station-swapping. The physical means by which these performance advantages are achieved is not fully understood. Suffice it to say that the improved directionless and distortionless qualities of the instrument panel antenna have been observed and documented.

Second, since the entire length and/or area of the antenna conductor is accessible for electrical connection, the instrument panel antenna can be coupled to the radio receiver from a point on the antenna conductor at which the output impedance of the antenna conductor most nearly matches the input impedance of the radio receiver. Accordingly, collected radio waves may be transferred from the instrument panel antenna to the radio receiver with minimum power loss.

Third, because the instrument panel antenna is located in close proximity to the radio receiver, the length of transmission line required to connect the antenna conductor to the radio receiver is extremely short. As a result, radio waves traveling over the transmission line from the antenna conductor to the radio receiver are not appreciably attenuated by the relatively small impedance of the line. Further, the comparatively trivial impedance of the transmission line ex erts negligible influence upon the impedance match between the instrument panel antenna and the radio receiver.

Fourth, the instrument panel antenna is better protected from damage by weather elements, by striking objects, and by mischievous vandals than either the mast antenna or the windshield antenna. I

Fifth, unlike the mast antenna and the windshield antenna, the instrument panel antenna does not detract in even the slightest manner from the artistic styling of the vehicle.

Sixth, since there is rarely a need to replace the in strument panel pad of the vehicle, the conductors of the instrument panel antenna are less likely to add to the cost of a vehicle replacement item than are the conductors of the windshield antenna.

Seventh, the instrument panel antenna may be impedance matched or trimmed to the radio receiver before the instrument panel assembly is installed within the vehicle thereby significantly increasing the ease with which the trimming operation may be accomplished.

These and other aspects and advantages of the invention may be best understood by reference to the following detailed description of a preferred embodiment when considered in conjunction with the accompanying drawing.

In the drawing:

FIG. 1 is a perspective view of an automotive vehicle equipped with an instrument panel antenna incorporating the principles of the invention.

FIG. 2 is a cross-sectional view of the instrument panel antenna embodiment shown in FIG. 1.

FIG. 3 is an exploded perspective view of the instrument panel antenna embodiment shown in FIGS. 1 and 2.

Referring to FIGS. 1 and 2, an automotive vehicle 10 includes a metal body structure 12 containing a windshield aperture or opening 14. Specifically, the windshield opening 14 is formed between an upper rearward edge 16 and a lower forward edge 18 which extend approximately horizontally across the exterior width of the vehicle 10 in generally parallel spaced relation to one another. A windshield 20 is mounted within the opening 14. The conductive body structure 12 forms a shield by which radio waves are prevented from entering the vehicle 10 from the outside. On the other hand, the windshield opening 14 forms a port in the body structure 12 through which radio waves are permitted to enter the vehicle 10.

An instrument panel assembly 22 is located within the vehicle 10 beneath the windshield opening 14. A top edge 24 of the instrument panel assembly 22 ex tends approximately horizontally across the interior width of the vehicle in generally parallel spaced relation to the upper and lower edges 16 and 18 of the windshield opening 14. As best shown in FIG. 2, the lower edge 18 of the windshield opening 14 is positioned forward of the top edge 24 of the instrument panel assembly 22 while the upper edge 16 of the windshield opening 14 is positioned rearward of the lower edge 18 of the windshield opening 14. Consequently, the windshield 20 overlays the instrument panel assembly 22 so that radio waves passing through the windshield opening 14 irradiate the space between the top edge 24 of the instrument panel assembly 22 and the lower edge 18 of the windshield opening 14.

Referring to FIG. 3, the instrument panel assembly 22 includes one or more metal mounting brackets, generally designated by the numeral 26, which are attached to the body structure 12 of the vehicle 10 for supporting various gauges, controls, and like instruments (not shown), including a radio receiver 28. The ratio receiver 28 is electrically grounded to the conduc tive vehicle body structure 12 through one or more of the conductive mounting brackets 26. The radio receiver may be an AM receiver, an AM/FM receiver or an AM/FM-Stereo receiver. Regardless of type, the radio receiver 28 is responsive to the application of radio waves at an input terminal 30 to produce derivative audio waves at an output terminal 32 which is connected to one or more monophonic or stereophonic speakers (not shown), as the case may be.

Further, the instrument panel assembly 22 includes an instrument panel pad 34 which is suitably attached to the mounting brackets 26 by various screws, nuts, clips and other suitable fasteners (not shown). As supported by the brackets 26, a top portion 34, of the instrument panel pad 34 extends under the windshield 20 of the vehicle 10. As best shown in FIG. 2, the instrument panel pad 34 comprises a rigid inner layer or base 36 which is preferably made of a molded plastic, a pliable outer layer or skin 38 which is preferably made of a sheet plastic, and a resilient intermediate layer or cushion 40 which is preferably made of a foamed plastic. However, it is to be understood that the present invention is not limited to the particular shape or structure of the illustrated instrument panel pad 34.

A wire conductor 42 is supported by the top portion 34, of the instrument panel pad 34 within the space permeated by radio waves passing through the windshield opening 14 of the vehicle 10. The conductor 42 extends from a terminal end 42,, to an open end 42,, in a loosely defined overlapping loop configuration. The terminal end 42,, of the conductor 42 is grounded to the vehicle body structure 12. A transmission line or coaxial cable 44 includes an outer conductor 46 and an inner conductor 48. The outer conductor 46 is grounded to the vehicle body structure 12. The inner conductor 48 couples the input 30 of the radio receiver 28 to a tap point 50 on the conductor 42 such that the conductor 42 serves as an antenna for the radio receiver 28. In operation, the conductor 42 electromagnetically abstracts energy from passing radio waves to inductively reproduce the radio waves along its length. The abstracted or collected radio waves are applied to the radio receiver 28 through the coaxial cable 44.

Referring to FIG. 2, the antenna conductor 42 is actually embedded within the top portion 34, of the instrument panel pad 34. Specifically, the conductor 42 is located beneath the outer skin 38 and on top of the inner base 36 where it is surrounded by the resilient cushion 40. In this position, the antenna conductor 42 is fully protected from deterioration by weather elements, from impact by striking objects, and from damage by vandals. Further, in this location, the antenna conductor 42 does not detract in even the slightest manner from the aesthetic appearance of the vehicle 10. Moreover, since the instrument panel pad 34 should never need replacement, the antenna conductor 42 does not add to the anticipated cost of maintaining the vehicle 10. Of course, the conductor 42 could as well be mounted on the undersurface of the inner base 36 or on the uppersurface of the outer skin 38. In either alternative location, the same protective, styling, and maintenance advantages would obtain.

As supported by the top portion 34, of the instrument panel pad 34, the conductor 42 exhibits some superior performance characteristics as a radio antenna. First, the audio quality of the radio receiver 28 is relatively independent of the direction of travel by the vehicle 10. Second, the audio quality of the radio receiver 28 is relatively immune from many forms of FM distortion, particularly station-swapping which occurs when the radio receiver suddenly shifts from the reception of one broadcast station to the reception of another broadcast station. The precise physical means by which these performance advantages are achieved is not fully understood. However, there is no doubt that these superior directionless and distortionless characteristics are manifested by the antenna conductor 42 as supported by the top portion 34, of the instrument panel pad 34.

As previously described, the antenna conductor 42 electromagnetically abstracts energy from passing radio waves to inductively reproduce the radio waves along the conductor 42 from which they are applied to the radio receiver 28 over the coaxial cable 44. By virture of this electromagnetic induction process, a varying distributed impedance is defined over the length of the conductor 42 between the terminal end 42,, and the open end 42,. To maximize the transfer of radio wave energy from the antenna conductor 42 to the radio receiver 28, it is desirable that the output impedance of the antenna conductor 42 as defined between the tap point 50 and ground be matched as nearly as possible to the input impedance of the radio receiver 28 as defined between the input terminal 30 and ground. Accordingly, since the entire length of the antenna conductor 42 is accessible for electrical connection, the tap point 50 at which the inner conductor 46 of the coaxial cable 44 is connected to the antenna conductor 42 may be selected such that the output impedance of the antenna conductor 42 most nearly matches the input impedance of the radio receiver 28. In addition, the impedance matching or trimming of the antenna conductor 42 to the radio receiver 28 may be performed before the instrument panel assembly 22 is installed within the vehicle 10 thereby to greatly facilitate the fulfillment of this important function.

As supported by the top portion 34, of the instrument panel pad 34, the antenna conductor 42 is located in close proximity to the radio receiver 28 which is mounted within the instrument panel assembly 22 directly beneath the conductor 42. Consequently, the length of the transmission line or coaxial cable 44 connecting the antenna conductor 42 to the radio receiver 28 is extremely short. As a result, radio waves traveling through the coaxial cable 44 from the antenna conductor 42 to the radio receiver 28 are not appreciably attenuated by the proportionately small impedance of the cable 44. Further, the relatively small impedance of the coaxial cable 44 has negligible effect upon the impedance match between the antenna conductor 42 and the radio receiver 28.

As previously described, the antenna conductor 42 is disposed in a loosely defined overlapping loop configu ration. However, it is to be understood that this particular antenna configuration is shown for demonstrative purposes only. The instrument panel antenna of this invention is not in any way limited to the illustrated conductor configuration. A multitude of diverse instrument panel antenna embodiments, employing a myraid of different sizes and shapes of wires, screens, foils and the like as the antenna conductor, were constructed and found to yield satisfactory performance. For example, another embodiment of an instrument panel antenna incorporating the principles of the invention is illustrated in copending U.S. Pat. application Ser. No. 368,539 which was filed concurrently with the present application and which is assigned to the assignee of the present application.

As a result of this rather extensive experimentation, it was concluded that apart from a minor dependency upon the specific conductor configuration, the performance of the instrument panel antenna of the invention is largely dependent upon the overall conductor area. In general, as conductor area is increased, AM reception is enhanced while FM reception eventually becomes degraded. An increase in conductor area apparently increases the effective length of the radio antenna thereby enhancing the reception of AM radio waves. Conversely, an increase in conductor area seemingly increases the capacitive loading between the radio antenna and the adjacent conductive body structure of the vehicle thereby degrading the reception of FM radio waves. By reason of having a much higher frequency, FM radio waves more than AM radio waves are susceptible to attenuation from capacitive loading of the antenna. Accordingly, is appears that the specific conductor configuration for the instrument panel antenna of the invention must be determined anew for each different vehicle model dependent upon the relative proximity of major portions of the conductive body structure to the antenna conductor.

What is claimed is:

1. In an automotive vehicle, the combination comprising: an instrument panel assembly having a top edge extending approximately horizontally across the interior width of the vehicle body; a conductive body structure forming a shield by which radio waves are normally prevented from entering the vehicle, the body structure including a windshield opening having a lower edge extending approximately horizontally across the exterior width of the vehicle body generally parallel to and spaced forward of the top edge of the instrument panel assembly and having an upper edge extending approximately horizontally across the exterior width of the vehicle body generally parallel to and spaced rearward of the lower edge of the windshield opening so that radio waves directed downward through the windshield opening from outside of the vehicle body pass through an irradiated space defined between the lower edge of the windshield opening and the top edge of the instrument panel assembly; a radio receiver mounted within the instrument panel assembly; a top portion of the instrument panel assembly extending within the irradiated space and including a nonconductive rigid inner layer, a nonconductive pliable outer layer, a nonconductive resilient intermediate layer interposed between the inner and outer layers, and a conductor physically disposed within the intermediate layer between the inner and outer layers for inductively collecting passing radio waves to provide an antenna which is protected from potentially damaging forces outside of the vehicle and which does not detract from the aesthetic appearance of the vehicle; and a transmission line for coupling the radio receiver to a point on the antenna conductor at which the output impedance of the antenna conductor is approximately matched to the input impedance of the radio receiver thereby to maximize the electrical efficiency with which radio waves are transferred from the antenna conductor to the radio receiver and wherein the close proximity of the antenna conductor to the radio receiver minimizes the length of the transmission line such that the amount of signal antennuation and impedance mismatch pro duced by the relatively small impedance of the transmission line is negligible. 

1. In an automotive vehicle, the combination comprising: an instrument panel assembly having a top edge extending approximately horizontally across the interior width of the vehicle body; a conductive body structure forming a shield by which radio waves are normally prevented from entering the vehicle, the body structure including a windshield opening having a lower edge extending approximately horizontally across the exterior width of the vehicle body generally parallel to and spaced forward of the top edge of the instrument panel assembly and having an upper edge extending approximately horizontally across the exterior width of the vehicle body generally parallel to and spaced rearward of the lower edge of the windshield opening so that radio waves directed downward through the windshield opening from outside of the vehicle body pass through an irradiated space defined between the lower edge of the windshield opening and the top edge of the instrument panel assembly; a radio receiver mounted within the instrument panel assembly; a top portion of the instrument panel assembly extending within the irradiated space and including a nonconductive rigid inner layer, a nonconductive pliable outer layer, a nonconductive resilient intermediate layer interposed between the inner and outer layers, and a conductor physically disposed within the intermediate layer between the inner and outer layers for inductively collecting passing radio waves to provide an antenna which is protected from potentially damaging forces outside of the vehicle and which does not detract from the aesthetic appearance of the vehicle; and a transmission line for coupling the radio receiver to a point on the antenna conductor at which the output impedance of the antenna conductor is approximately matched to the input impedance of the radio receiver thereby to maximize the electrical efficiency with which radio waves are transferred from the antenna conductor to the radio receiver and wherein the close proximity of the antenna conductor to the radio receiver minimizes the length of the transmission line such that the amount of signal antennuation and impedance mismatch produced by the relatively small impedance of the transmission line is negligible. 